Cathode ray tube



1940' K. SCHLESINGER ,00

CATHODE RAY TUBE Original Filed 0ct. 12, 1933 Jm e/r/or Patented Dec. 31, 1940 U iTEosTATEs CATHOD'E RAY TUBE Kurt Schlesinger, Berlin, Germany assignor, by

mesne assignments, to Loewe Radio, Inc., a corporation of New York Original application October 12, 1933, Serial No. 693,303. Divided and this application January 7, 1936, Serial No. 57,871. In Germany October 1 Claim.

It is already known to metallize the luminous screen of Braun tubes, and to connect up the same with a constant potential. On the other hand it'has already been proposed to furnish the wall of the Braun tube with a metallic coating, and to earth this coating or to link up the same with the maximum potential occurring in the tube and in this case to use it as an after-acceleration anode.

The appilcant has found that both in the case in which the conductive wall coating as well as in the case in which the metallized screen is employed as after-acceleration anode the image points are not sharply formed. If furthermore the coating-such as usual heretofore-extends to within close proximity of the first anode, the high potential thereof exerts undesirable effects on the ray.

The widening out of the image point may in these cases be explained by absence of the return-current electron cloud, which also exerts a certain concentrating effect.

The applicant has found that the concentrating effect of the return-current electrons may be Wholly replaced by the effect of a conductor raised to a suitable potential which is' weakly negative in relation to the ray. This conductor may conveniently be constructed in the form of a preferably narrow metallic strip (for example, silvered strip) arranged on the wall of the tube. The width of the conductor is so chosen that the field thereof exerts no noticeable efiect on the ray in the vicinity of the anode. In the case of a tube of 30 cm. in length, 6 cm. diameter of the neck and 18 cm. diameter of the bottom the width of the strip in accordance with the invention can be selected at 5.cm., i. e., at approximately of the length of the tube.

If now this conductor is raised to a suitable potential, which is weakly negative in relation to the ray, the image screen may be tapped without an increase taking place in the width of the image point. 1

According to the invention, the metallized image screen is now employed as after-acceleration anode (second anode) by the application of a suitable high positive potential.

The following potentials in operation have been found suitable in connection with a tube of the dimensions set forth above:

1st anode=1000 volts, metallized auxiliary conductor=900 volts, I 2nd anode=3000 volts,

Naturally the tubes according to the invention may also be operated with other potentials;

these potentials, however, must always be selected in such fashion that the auxiliary conductor always possesses a negative potential in relation to the ray.

It is to be observed that the auxiliary conductor should not be made too weakly negative in relation to the after-acceleration anode, as otherwise the ray Will be bent off in the vicinity of the auxiliary conductor, which in. the case of television tubes takes effect in the form of a rounding of the image.

The tube according to the invention is of particular importance for use with so-called residual gas filling, i. e., a gas pressure of not more than 10- mm.

A form of embodiment of the tube according to the invention is illustrated by way of example in the drawing. In the latter I is the body of the tube, 2 the first anode, and 3 an auxiliary conductor according tothe invention, which may be arranged in the vicinity of the image screen, possesses a weakly negative potential in relation to the ray, and is made so narrow that it is unable .to exert any disturbing effect on the ray in the vicinity of the first anode. 4 is the metallized image screen, which in accordance with the invention is employed as after-acceleration anode. 5 and 6 are the leads passing to the auxiliary conductor and the image screen.

The most favourable potentials vary in respect of different forms and sizes of tubes, and. may be adjusted without difficulty in each single case.

The combination of a tube according to the present invention with suitable potential supplying means has been claimed in the co-pending parent application to the present one, Ser. No. 693,303, filed October 12, 1933.

I claim:

A cathode ray tube device comprising an elongated envelope having an end wall and a side wall portion, the said end wall being substantially normal to the longitudinal axis of the elongated envelope and having a transversedimension of the order of three-fifths of the length of the envelope, a conducting coating adapted to luminesce under electron impact covering substantially the end wall only of the said envelope, an electron gun supported within the envelope substantially on the longitudinal axis and at substantially the end of the envelope remote from the conducting end wall for developing an electron beam to impact said conducting .coa-ting, beam deflecting means for moving the electron beam across the said conducting end wall, said deflecting means being located intermediate the electron gun and the end of the envelope having the conducting coating, and one and only one tubular auxiliary electrode positioned within the envelope intermediate the conducting end wall and the beam defleeting means and substantially parallel to the tube wall, said auxiliary electrode having open ends and electrically separated from the said conducting end wall and having a longitudinal length less than one-sixth of the length of the tube envelope, said auxiliary electrode being adapted to be maintained slightly negative relative'the electron gun anode.

KURT SCI-ILESINGE'R. 

